The construction of a "unitized vehicle body" commences with the formation of individual major body panels by stamping the panels from a sheet metal blank. Typically, these major panels include a floor panel, right and left body side panels, a fire wall, and either a roof panel or transversely-extending header members on which a roof panel is subsequently mounted. After the individual panels are stamped, some preliminary assembly operations may then be performed on the individual panels, such as, for example, adding door hinge and latch hardware to body side panels at appropriate locations proximate the door opening, adding seat-mounting brackets and reinforcements to the floor panel, et cetera.
Next, a set of panels that together constitute a sub-assembly of the finished vehicle body is then loosely assembled together. This initial loose assembly of panels frequently is accomplished by a "toy tab" arrangement in which one or more panels is formed with a tab which projects from an edge and which is received in a slot of an adjacent panel. This technique interlocks the panels and frame members to each other to thereby form a preliminary, loosely-assembled vehicle body wherein the panels and frame members will not separate from each other, but the panels and frame members may tilt or move relative to one another. This initial loosely-assembled sub-assembly is then brought to a welding station where the various panels and frames are welded to each other in a rigid, permanently assembled relationship.
This initial welding operation step is one of the most important steps in the assembly of the vehicle body because it establishes the final welded alignment of the various panels and headers relative to each other, which is essential to subsequent assembly operations performed on the sub-assembly. During the welding operation, it is desirable that the various panels and headers be precisely and accurately located and aligned relative to one another and be held fixedly in the desired position. The positioning of the various panels and header members during the welding operation is accomplished by clamping frames which carry a plurality of individual clamps arranged thereon to clamp various body components in the desired position.
It is desirable to perform as many welding operations as possible within the same welding station since the relative positioning of the various panels and headers is critical to the ability to precisely relocate and reclamp the vehicle body at subsequent stations along the production line. Due to variations between assembly stations and variation and movement of the various panels and headers, it is impossible to subsequently relocate and reclamp the vehicle body without inadvertently stacking up tolerances or creating variances between the relative positioning of the various panels and headers. Therefore, it is desirable to frame as much of the vehicle body as possible within the same welding station so that a maximum number of welding operations can be performed on the vehicle body without having to subsequently reclamp and relocate the vehicle body since reclamping and relocating may increase the tolerances between the relative positions of the various panels and headers of the vehicle body and decrease the repeatability between consecutive vehicle bodies in the production line.
To accomplish multiple welds, programmable robotic welders have been used to perform several welds at different locations on a vehicle body at a single welding station. The programmable robotic welders are typically located at a welding station and on opposite sides of the conveyor line passing through the welding station. When the vehicle body sub-assembly is conveyed to and positioned at the welding station, the head of one welder may, for example, be extended to pass through the vehicle door opening to apply several tack welds along the seam between the vehicle body side panel and the vehicle body floor panel. In situations where the clamping frames are positioned at opposite sides of the vehicle body, clearance problems can arise and may restrict the range of motion of the welding head that must first pass through the clamping frame before the welding head can gain access to the vehicle body. Welding head access problems can require that the portions of the vehicle body that cannot be accessed by the welding head at the first welding station must instead be accessed at a subsequent, second welding station. This is an undesirable situation, since the vehicle body must be relocated and reclamped at a subsequent, second welding station, thereby increasing the likelihood of tolerance buildup between the relative positions of the various panels and headers of the vehicle body and also decreasing the repeatability between consecutive vehicle bodies in the production line.
Another problem arises when separate clamping frames are employed at opposite sides of the vehicle body, since the two clamping frames must be independently located in a predetermined relationship relative to each other and to the position occupied by the vehicle body that the frames are to clamp in place. Since the two separate clamping frames are not directly connected to one another, the frames must use a common positional reference that is either defined by a spatial orientation or by a fixture or linkage assembly. These types of two-frame systems exhibit problems with repeatability, since two-frame referencing techniques inherently create tolerance build-ups within the systems due to repeated movements, thermal expansion and contraction, mechanical wear, et cetera. Also, when separate clamping frames are changed to accommodate different vehicle body styles or configurations, the problems with repeatability can be further magnified, which is undesirable.
In the automotive industry today, it is common for one particular car model to have several different body styles. Accommodating each body style requires clamping and welding different body locations as well as gaining access to different body areas so that the clamping and welding apparatus can be properly positioned while extending through the clamping frame. To avoid the situation of having to supply separate production lines and welding stations for the different body styles of a particular car model, it is desirable to provide a single welding station that can be adapted to accommodate a plurality of different body styles in a quick and efficient manner while ensuring the accuracy and repeatability that are required of the welding operation.